WASHINGTON (AP) - President Barack Obama rolled to re-election Tuesday night, vanquishing former Massachusetts Gov. Mitt Romney and prevailing despite a weak economy that plagued his first term and put a crimp in the middle class dreams of millions

"This happened because of you. Thank you" Obama tweeted to supporters as he celebrated four more years in the White House.

After the costliest - and arguably the nastiest - campaign in history, divided government seemed alive and well.

Democrats retained control of the Senate with surprising ease. Republicans were on course for the same in the House, making it likely that Speaker John Boehner of Ohio, Obama's partner in unsuccessful deficit talks, would reclaim his seat at the bargaining table.

Romney led narrowly in the popular vote, by about 30,00 votes out of more than 98 million cast, with ballots counted in 74 percent of the nation's precincts.

But Obama's laserlike focus on the battleground states allowed him to run up a sizeable margin in the competition for electoral votes, where it mattered.

He won Ohio, Wisconsin, Virginia, Iowa, New Hampshire, Colorado and Nevada, seven of the nine battlegrounds where the rivals and their allies poured nearly $1 billion into dueling television commercials.

Romney was in Massachusetts, his long and grueling bid for the presidency at an unsuccessful end.

He won North Carolina among the battleground states. Florida remained too close to call.

The election emerged as a choice between two very different visions of government - whether it occupies a major, front-row place in American lives or is in the background as a less-obtrusive facilitator for private enterprise and entrepreneurship.

The economy was rated the top issue by about 60 percent of voters surveyed as they left their polling places. But more said former President George W. Bush bore responsibility for current circumstances than Obama did after nearly four years in office.

That bode well for the president, who had worked to turn the election into a choice between his proposals and Romney's, rather than the simple referendum on the economy during his time in the White House.

Unemployment stood at 7.9 percent on election day, higher than when he took office. And despite signs of progress, the economy is still struggling after the worst recession in history.

There was no doubt about what drove voters to each candidate.

About 4 in 10 said the economy is on the mend, but more than that said it was stagnant or getting worse more than four years after the near-collapse of 2008. The survey was conducted for The Associated Press and a group of television networks.

In the battle for the Senate, Democrats won seats currently held by Republicans in Indiana and Massachusetts.

Polls were still open in much of the country as the two rivals began claiming the spoils of a brawl of an election in a year in which the struggling economy put a crimp in the middle class dreams of millions.

The president was in Chicago as he awaited the voters' verdict on his four years in office. He told reporters he had a concession speech as well as victory remarks prepared. He congratulated Romney on a spirited campaign. "I know his supporters are just as engaged, just as enthusiastic and working just as hard today" as Obama's own, he added.

Romney reciprocated, congratulating the man who he had campaigned against for more than a year.

Earlier, he raced to Ohio and Pennsylvania for Election Day campaigning and projected confidence as he flew home to Massachusetts. "We fought to the very end, and I think that's why we'll be successful," he said, adding that he had finished writing a speech anticipating victory but nothing if the election went to his rival.

But the mood soured among the Republican high command as the votes came in and Obama ground out a lead in critical states.

Like Obama, Vice President Joe Biden was in Chicago as he waited to find out if he was in line for a second term. Republican running mate Paul Ryan was with Romney in Boston, although he kept one eye on his re-election campaign for a House seat in Wisconsin, just in case.

The long campaign's cost soared into the billions, much of it spent on negative ads, some harshly so.

In the presidential race, an estimated one million commercials aired in nine battleground states where the rival camps agreed the election was most likely to be settled - Ohio, New Hampshire, Virginia, Florida, North Carolina, Wisconsin, Iowa, Colorado and Nevada.

In a months-long general election ad war that cost nearly $1 billion, Romney and Republican groups spent more than $550 million and Obama and his allies $381 million, according to organizations that track advertising.

In Virginia, the polls had been closed for several minutes when Obama's campaign texted a call for volunteers "to make sure everyone who's still in line gets to vote."

In Florida, there were long lines at the hour set for polls to close. Under state law, everyone waiting was entitled to cast a ballot.

According to the exit poll, 53 percent of voters said Obama is more in touch with people like them, compared to 43 percent for Romney.

About 60 percent said taxes should be increased, taking sides on an issue that divided the president and Romney. Obama wants to let taxes rise on upper incomes, while Romney does not.

Other than the battlegrounds, big states were virtually ignored in the final months of the campaign. Romney wrote off New York, Illinois and California, while Obama made no attempt to carry Texas, much of the South or the Rocky Mountain region other than Colorado.

There were 33 Senate seats on the ballot, 23 of them defended by Democrats and the rest by Republicans.

The GOP needed a gain of three for a majority if Romney won, and four if Obama was re-elected. Neither Majority Leader Harry Reid of Nevada nor GOP leader Mitch McConnell of Kentucky was on the ballot, but each had high stakes in the outcome.

All 435 House seats were on the ballot, including five where one lawmaker ran against another as a result of once-a-decade redistricting to take population shifts into account. Democrats needed to pick up 25 seats to gain the majority they lost two years ago.

Depending on the outcome of a few races, it was possible that white men would wind up in a minority in the Democratic caucus for the first time.

Obama was elected the first black president in 2008, and four years later, Romney became the first Mormon to appear on a general election ballot. Yet one man's race and the other's religion were never major factors in this year's campaign for the White House, a race dominated from the outset by the economy.

Over and over, Obama said that during his term the nation has begun to recover from the worst recession since the Great Depression. While he conceded progress has been slow, he accused Romney of offering recycled Republican policies that have helped the wealthy and harmed the middle class in the past and would do so again.

Romney countered that a second Obama term could mean a repeat recession in a country where economic growth has been weak and unemployment is worse now than when the president was inaugurated. A wealthy former businessman, he claimed the knowledge and the skills to put in place policies that would make the economy healthy again.

In a race where the two men disagreed often, one of the principal fault lines was over taxes. Obama campaigned for the renewal of income tax cuts set to expire on Dec. 31 at all income levels except above $200,000 for individuals and $250,000 for couples.

Romney said no one's taxes should go up in uncertain economic times. In addition, he proposed a 20 percent cut across the board in income tax rates but said he would end or curtail a variety of tax breaks to make sure federal deficits didn't rise.

The differences over taxes, the economy, Medicare, abortion and more were expressed in intensely negative advertising.

Obama launched first, shortly after Romney dispatched his Republican foes in his quest for the party nomination.

One memorable commercial showed Romney singing an off-key rendition of "America The Beautiful." Pictures scrolled by saying that his companies had shipped jobs to Mexico and China, that Massachusetts state jobs had gone to India while he was governor and that he has personal investments in Switzerland, Bermuda and the Cayman Islands.

Romney spent less on advertising than Obama. A collection of outside groups made up the difference, some of them operating under rules that allowed donors to remain anonymous. Most of the ads were of the attack variety. But the Republican National Committee relied on one that had a far softer touch, and seemed aimed at voters who had been drawn to the excitement caused by Obama's first campaign. It referred to a growing national debt and unemployment, then said, "He tried. You tried. It's OK to make a change."

More than 30 million voters cast early ballots in nearly three dozen states, a reflection of the growing appeal of getting a jump on the traditional Election Day.